Fix the documentation of the metrics setting (#10978)

openmetrics/README.md

@@ -24,7 +24,7 @@ For each instance the following parameters are required:
 | ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
 | `openmetrics_endpoint` | The URL where your application metrics are exposed by Prometheus (must be unique).                                                                                                                         |
 | `namespace`      | The namespace to prepend to all metrics.                                                                                                                                                                                                                                 |
-| `metrics`        | A list of metrics to retrieve as custom metrics. Add each metric to the list as `metric_name` or `metric_name: renamed` to rename it. Use `*` as a wildcard (`metric*`) to fetch all matching metrics. **Note**: Wildcards can potentially send a lot of custom metrics. |
+| `metrics`        | A list of metrics to retrieve as custom metrics. Add each metric to the list as `metric_name` or `metric_name: renamed` to rename it. The metrics are interpreted as regular expressions. Use `.*` as a wildcard (`metric.*`) to fetch all matching metrics. **Note**: Regular expressions can potentially send a lot of custom metrics. |
 
 **Note**: This is a new default OpenMetrics check example. If you previously implemented this integration, see the [legacy example][5].